The present invention relates to a nozzle head for use in an ink jet printer.
A nozzle head having the features specified in the preamble of claim 1 is disclosed in EP-A-0 402 172. This nozzle head comprises a channel plate defining a linear array of equidistant nozzles and a plurality of parallel ink channels, each connected to a respective one of the nozzles. On one side of the channel plate there is disposed an array of elongate fingers projecting towards the nozzle plate and extending in parallel with the ink channels. The ends of these fingers facing away from the channel plate are interconnected by a bridge portion which is formed integrally with the fingers. The fingers and the bridge portion are made of a piezoelectric ceramic material. Every second finger is provided with electrodes and serves as an actuator which, when a print signal is applied to the electrodes, compresses the ink liquid contained in the associated ink channel, so that an ink droplet is expelled from the nozzle. The other fingers intervening between the actuators serve as support members which rigidly connect the channel plate to the bridge portion, so that latter may function as a backing means for receiving the reaction forces generated by the actuators.
Since a support member is provided between each pair of consecutive actuators, each actuator is substantially shielded against the reaction forces from its neighbors, so that undesired cross-talk between the various channels is reduced.
However, when one of the actuators is activated, e.g. expanded, the support members adjacent thereto on both sides are elastically deformed to some extent, so that the bridge portion is slightly deflected. This effect becomes more significant when a plurality of neighboring actuators are activated simultaneously, whereby the stresses applied to the bridge portion are accumulated. In this case the deformation of the bridge portion will also affect the actuators which are disposed at a comparatively large distance from the active actuators and will cause the generation of parasitic acoustic waves in the ink channels where no droplets are to be expelled. Thus, there exists a problem which can be termed "long-range cross-talk."
It is an object of the present invention to provide a nozzle head in which long-range cross-talk can be suppressed more efficiently. According to the present invention, the backing means comprise a separate backing member disposed over the array of fingers, said backing member being more flexible in the transverse direction of the ink channels than in the longitudinal direction thereof.
As a result, the reaction force of each of the actuators of one block is mainly absorbed by the directly adjacent support members, whereby the mechanical coupling between actuators separated by a large distance is reduced due to the flexibility of the backing member. Thus, the undesired long-range cross-talk phenomenon is substantially eliminated.
In addition, the manufacture of the array of fingers and of the backing means is facilitated, because only the actuators have to be made of a piezoelectric material whereas the material of the separate backing member may be selected as desired in order to optimize the mechanical properties thereof. Moreover, part of the electrodes needed for energizing the actuators can be arranged at the boundary between the actuators and the backing member, so that the electrodes can easily be disposed at appropriate positions relative to the actuators and/or the pattern of electrical leads for energizing the electrodes is simplified.
The ends of the fingers (actuators and support members) adjacent to the backing member may still be interconnected by relatively thin bridge portions formed integrally with the fingers. Alternatively, the fingers may be separated completely so that they are interconnected only by the backing member disposed thereon.
The unisotropic flexibility characteristic of the backing member can be achieved for example by providing a plate with a suitable profile on the side opposite to the array of fingers.
In a preferred embodiment, the backing member has a grid-like structure and comprises a plurality of beams extending in the longitudinal direction of the ink channels. Preferably, the width of the beams is made so large that each beam supports only a few fingers, i.e. at least one support member and at least one actuator. Thus, the reaction force of an actuator is transmitted to the neighboring support member (s) via the associated beam, without causing a substantial displacement of the neighboring beams and the actuators supported thereby.
The backing member may further comprise transverse beams interconnecting the ends of the longitudinal beams, thereby stabilizing the longitudinal beams against tilting movements about their longitudinal axis.
In a particularly preferred embodiment, the array of fingers is formed by a number of separate blocks each of which comprises only a few fingers integrally connected with each other and supported by a common beam. Each block advantageously comprises only one support member and only one or two actuators, so that the spatial relationship between the actuators and the associated support members is the same for all actuators (except for mirror symmetry in the case of two actuators disposed on opposite sides of the support member). Then, the support structure for the various actuators will not cause any differences in the performance and mechanical behavior of the actuators in the process of droplet generation.
An efficient method for manufacturing a nozzle head of the type discussed hereinabove comprises bonding a comparatively thick layer of piezoelectric material to a surface of an essentially plate-like member, which will later form the backing member. Then, an array of fingers is formed by cutting parallel grooves into a layer of piezoelectric material. The depth of the grooves separating individual fingers of the same block is made smaller than the thickness of the layer of piezoelectric material, whereas the grooves which are to separate the blocks from each other are cut to a greater depth so that they extend into the backing member, thereby dividing the backing member into separate beams.